This application claims benefit and priority from the following application: Japanese Patent Application No. P2003-008914, filed Jan. 16, 2003, the contents of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle headlamp arranged to emit low beams of light, using a projector type lighting device unit.
2. Background of the Related Art
In the related art, vehicle headlamps for emitting light forward from vehicles use projector type lighting device units. The related art projector type lighting device unit is designed to converge rays of light from a light source disposed on an optical axis extending in the longitudinal direction of a vehicle closer to the optical axis, and to reflect the light forward by means of a reflector. As a result, the reflected light is emitted in the forward direction of a lighting device through a projection lens installed in front of the reflector.
When the projector type lighting device unit is used as a lighting device unit for emitting low beams of light, a shade is provided between the projection lens and the reflector to shield part of rays of the light reflected from the reflector.
In connection with the foregoing related art arrangement, related art JP-Y2-2558801 (Japanese Registered Utility Model Publication Number: 2558801), the contents of which is incorporated herein by reference, discloses a projector type lighting device unit for emitting low beams of light. The projector type lighting unit includes a shade having a spherical reflective surface centering on a light source formed on the back side of the shade. Additional related art, the contents of which is also incorporated herein by reference, includes JP-A-2002-175709 (Japanese Application Publication Number: 2002-175709), and U.S. Pat. No. 4,800,467.
In such a related art projector type lighting device unit for emitting low beams of light, most of the light reflected in the lower reflective region of the reflector and directed to the projection lens is shielded by the shade. Therefore, a related art problem arises from low efficiency in utilizing the luminous flux of the light source.
However, as described in the above-identified JP-Y2-2558801 reference, light incident on a spherical reflective surface formed on the back side of the shade from the light source is sent back to the position of the light source, whereby the retroreflective light can be utilized as light incident on the upper reflective region of the reflector.
Since the light source has a fixed size, the retroreflective light from the spherical reflective surface spreads considerably, as compared with direct light from the light source. Therefore, a luminous distribution pattern formed by the retroreflective light reflected in the upper reflective region of the reflector becomes less uniform in the luminous intensity distribution.
Accordingly, the foregoing related art has various problems and disadvantages. For example, but not by way of limitation, light distribution control utilizing the retroreflective light is performs extremely poorly.